Special issue on ultrafast electron and molecular dynamics

Abstract

In the last few years, the advent of novel experimental and theoretical approaches has made possible the investigation of (time-resolved) molecular dynamics in ways not anticipated before. Experimentally, the introduction of novel light sources such as high-harmonic generation (HHG) and XUV/x-ray free electron lasers, and the emergence of novel detection strategies, such as time-resolved electron/x-ray diffraction and the fully coincident detection of electrons and fragment ions in reaction microscopes, has significantly expanded the arsenal of available techniques, and has taken studies of molecular dynamics into new domains of spectroscopic, spatial and temporal resolution, the latter including first explorations into the attosecond domain, thus opening completely new avenues for imaging electronic and nuclear dynamics in molecules. Along the way, particular types of molecular dynamics, e.g., dynamics around conical intersections, have gained an increased prominence, sparked by the realization of the essential role that this dynamics plays in relaxation pathways in important bio-molecular systems. In the short term, this will allow one to uncover and control the dynamics of elementary chemical processes such as, e.g., ultrafast charge migration, proton transfer, isomerization or multiple ionization, and to address new key questions about the role of attosecond coherent electron dynamics in chemical reactivity. The progress on the theoretical side has been no less impressive. Novel generations of supercomputers and a series of novel computational strategies have allowed nearly exact calculations in small molecules, as well as highly successful approximate calculations in large, polyatomic molecules, including biomolecules. Frequent and intensive collaborations involving both theory and experiment have been essential for the progress that has been accomplished.The special issue ‘Ultrafast electron and molecular dynamics’ seeks to provide an overview of the current developments, as well as new concepts that are emerging in this field when studying molecular dynamics at attosecond or few-femtosecond time-scales. It also aims at indicating how such studies are likely to evolve in the coming years. In this context, the present special issue contains contributions from recognized experts on HHG, free electron lasers, attosecond and femtosecond pump–probe spectroscopy, electron and x-ray diffraction methods, photoionization and theoretical methods specially designed for the analysis of experiments in this field. Seven review articles report on the present status of some selected topics, namely, table-top and free-electron lasers operating in the XUV and x-ray wavelength regimes to investigate ultrafast molecular dynamics, imaging methods to visualize electron and nuclear dynamics, nonlinear optics applications, and recent theoretical developments. These and other topics are covered by 32 research papers, in which new exciting results show the path for future developments in this field.